Laptop display stays black when on

Hello Techspot users.
Ive had my laptop for about one year and 8 months and never had any problems until a week ago. I turned my laptop on and nothing came on on the display. I took the battery our and turned it on with just the AC cord and it worked fine. then i put the battery back on and it worked. After this it happened to me the next two days and that same trick worked. a couple days ago it didn't work. I turned my laptop on and it was the screen was black. i could see the HDD activity light working and the power light was on so i knew it wasn't the HDD. i tried the trick but nothing happened. i can see the backlight is on but the screen is black. i thought the video card could be it but when i plug the laptop to an external monitor it works fine. I checked device manager and there seems to be no problems. I thought the video cables could have been loose so i opened up the laptop bezel and they are connected correctly. Does anybody know what is up? Is my screen done or could it be the cables? I haven't opened up the rest of the laptop so it could be that they are damaged under the hood.

Can I assume that you have used th fn key to toggle between LCD and external displays? Can you see any image if you shine a flashlight on the LCD panel? Besides cables, and good external display, the LCD display panel has to be bad